1. Field of the Invention
This invention pertains to an emergency roadside communication system and to a device for the same, and more particularly to a system with individual devices displaced along the side of a road for contacting a central station, such as a police station, to obtain emergency services.
2. Description of the Prior Art
It is important to provide communication devices along major roads and highways which can be used by motorists, and other members of the public to obtain car services, to notify police of a crime, or an accident, and/or to obtain various other types of emergency services. Such devices are typically placed at regular intervals. However the cost of such devices including installation and an associated interconnection is quite prohibitive, especially since each device is used relatively infrequently.
The present roadside communication systems fall into either of two categories; either radio-type system or hardwire systems. The radio-type systems comprise roadside devices which are two-way radio transceivers. All communications occur over the air at radio frequencies. However, inherently this type of communication is unreliable because it is adversely affected by weather conditions, especially for systems in which there is a large distance between the roadside devices and the central station. Furthermore, due to the advent of CB (citizen band) radios, the number of frequencies available, emergency for emergencies, is very limited. Thus, distance from the central station, dependence on weather conditions, and overcrowding of the radio frequencies render this type of communication undesirable for the intended use.
The second, or wire-type systems comprise roadside devices which are connected to a central station by actual voice-grade wires. The simplest of such systems require a dedicated pair of wires between the central system and each device in a typical star arrangement. While the roadside devices themselves are fairly inexpensive and reliable, the cost of providing, installing and manufacturing the large network of wires is prohibitive. More complicated systems make use of only two or four wires, so that the cost of providing, installing and manufacturing them is reduced drastically compared to the previous system. However, there is an increase of at least one magnitude in the complexity of both the roadside devices and the central system because now the devices are interconnected in a daisy chain, so that one kind of multiplexing scheme is necessary for communication.
A further disadvantage of the prior art systems is that customized equipment must be provided at the roadside and the central station. Differences between particular requirements of each system require customization further increasing the overall cost of the system. Additions to the present systems usually lead to further complications. Frequently new features or devices can be added only by retrofitting whole systems. Furthermore, the uniqueness and complexity of the systems make them hard to troubleshoot and requires special training of the repair personnel.